Atomic Structure

Question 1

What did Robert Boyle propose?

Answer 1

That there were some substances that could not be made simpler- the chemical elements

Question 2

What did John Dalton propose?

Answer 2

That elements were composed of invisible atoms. All the atoms of a particular element had the same mass and atoms of different elements had different masses. Atoms could not be broken down

Question 3

What did Henry Becquerel discover in 1896?

Answer 3

Radioactivity which showed that particles could come from inside the atom and therefore the atom was not invisible

Question 4

In 1897, what did J J Thomson discover?

Answer 4

The electron. He showed that electrons were negatively charged and electrons from all elements were the same

Question 5

What did Ernest Rutherford discover?

Answer 5

That most of the mass and all the positive charge of the atom was in a tiny central nucleus

Question 6

What are protons and neutrons sometimes called?

Answer 6

Nucleons because they’re found in the nucleus

Question 7

What is the relative mass of a proton?

Answer 7

1

Question 8

What is the relative mass of a neutron?

Answer 8

1

Question 9

What is the relative mass of an electron?

Answer 9

1/1840

Question 10

What is the relative charge of a proton?

Answer 10

+1

Question 11

What is the relative charge of a neutron?

Answer 11

0

Question 12

What is the relative charge of an electron?

Answer 12

-1

Question 13

What force holds protons and neutrons together in the centre of the atom?

Answer 13

The strong nuclear force which is much stronger than electrostatic forces of attraction that hold electrons and protons together in the atom

Question 14

What does the number of electrons in the outer shell of an atom determine?

Answer 14

The atom’s chemical properties and what sort of element it is

Question 15

What makes up the mass number (A) of an atom?

Answer 15

The total number of protons and neutrons in the nucleus

Question 16

What is an isotope?

Answer 16

An atom with the same number of protons but different numbers of neutrons

Question 17

Why do isotopes of the same element react chemically in exactly the same way?

Answer 17

Because they have the same electronic configuration

Question 18

Why do isotopes of the same element vary in mass?

Answer 18

Because they have different numbers of neutrons in their nuclei

Question 19

What did Niels Bohr propose in 1913?

Answer 19

That the atom consisted of a tiny positive nucleus orbited by negatively-charged electrons. The electrons orbited in shells of fixed size and the movement of electrons from one shell to the next explained how atoms absorbed and gave out light

Question 20

Who discovered the neutron in 1932?

Answer 20

James Chadwick

Question 21

What ideas did Gilbert Lewis put forward about how electrons allowed atoms to bond together?

Answer 21

• the inertness of noble gases was related to their having full outer shells of electrons
• ions were formed by atoms losing or gaining electrons to attain full outer shells
• atoms could also bond by sharing electrons to form full outer shells

Question 22

How many electrons can the first electron shell hold?

Answer 22

Up to 2 electrons

Question 23

How many electrons can the second shell?

Answer 23

Up to 8 electrons

Question 24

How many electrons can the third shell hold up to?

Answer 24

Up to 18 electrons

Question 25

What is the mass spectrometer used for?

Answer 25

It is used to determine relative atomic masses (Ar)

Question 26

What are relative atomic masses measured on a scale of?

Answer 26

They're measured on a scale on which the mass of an atom of Carbon-12 is defined as exactly 12

Question 27

How do you work out the Ar?

Answer 27

Average mass of 1 atom / 1/12th mass of 1 atom of Carbon-12

Question 28

How are mass spectrometers used by forensics scientists?

Answer 28

To identify substances such as illegal drugs

Question 29

Why is the TOF apparatus kept under a high vacuum?

Answer 29

To prevent ions that are produced colliding with molecules from the air

Question 30

How are ions formed in TOF spectrometry?

Answer 30

The sample to be investigated is dissolved in a volatile solvent and forced through a fine hollow needle that is connected to the positive terminal of a high voltage supply. This produces tiny positively charged droplets which have lost electrons to the positive charge of the supply. The solvent evaporates from the droplets into the vacuum until only a single positively charged ion is left behind

Question 31

Describe the acceleration stage of TOF spectrometry:

Answer 31

The positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed

Question 32

Describe the ion drift stage of TOF spectrometry

Answer 32

The ions pass through a hole in the negatively charged plate, forming a beam and travel along a tube, called the flight tube, to a detector

Question 33

How are ions detected in TOF spectrometry?

Answer 33

When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. The flight times are recorded. The positive ions pick up an electron from the detector which causes a current to flow

Question 34

How are the flight times analysed in TOF spectrometry?

Answer 34

The signal from the detector is passed to a computer which generates a mass spectrum

Question 35

What can the mass spectrometer be used to identify?

Answer 35

Different isotopes that make up an element

Question 36

How does a mass spectrometer detect different isotopes separately?

Answer 36

It detects individual ions so different isotopes are detected because they have different masses

Question 37

What do the solutions to the Schrödinger equation give?

Answer 37

The probability of finding an electron in a given volume of space called an atomic orbital

Question 38

What is the definition of ionisation energy?

Answer 38

Ionisation energy is the energy required to remove a mole of electrons from a mole of gaseous atoms

Question 39

What is the general trend in ionisation energies across a period?

Answer 39

Ionisation energies generally increase across a period because the nuclear charge is increasing which makes it more difficult to remove an electron

Question 40

Why is there a decrease in First IE between magnesium and aluminium?

Answer 40

Because the outer electron in aluminium is in a 3P orbital which is of a slightly higher energy than the 3S orbital. It therefore needs less energy to remove it

Question 41

Why is there a decrease in First IE values between phosphorus and sulfur?

Answer 41

In phosphorus, each of the three 3P orbitals contains just one electron whereas in sulfur, one of the 3P orbitals contains 2 electrons. The repulsion between these paired electrons makes it easier to remove one of them despite the increase in nuclear charge

Question 42

What is the general trend in First ionisation energies down group 2?

Answer 42

There is a general decrease down group 2 because the outer electron is in a main level that gets further from the nucleus in each case and increased shielding of nuclear charge